Marathon Bombings

BOSTON (CBSNewYork/AP) – One of the explosive devices used in the bombings of the Boston Marathon appeared to have been in a metal pressure cooker packed with nails and ball bearings, CBS News reported.

As CBS 2’s Lou Young reported, a law enforcement source told CBS News that one of the explosive devices appeared to have been placed in a metal pressure cooker which had been placed in a black nylon bag or backpack.

Investigators also found pieces of an electronic circuit board possibly indicating a timer was used in the detonation of the bomb.

The two bombs that exploded were made to look like discarded property, a law enforcement official told CBS News. It is still unknown if one or both bombs were in garbage cans. One may have been on the sidewalk.

The bombs were described as “low explosive,” but with “anti-personnel” packing. This is consistent with doctors reporting shrapnel pulled from victims. The official said there were apparently things like BBs, ball bearings and nails in the bombs.

While no information has been released about whether the attack was domestic or international in nature, authorities have noted that the pressure cooker design for the bombs is favored by al-Qaeda.

Similar pressure-cooker explosives have been used in Afghanistan, India, Nepal and Pakistan, according to a July 2010 intelligence report by the FBI and Homeland Security. Also, one of the three devices used in the May 2010 Times Square attempted bombing was a pressure cooker, the report said.

“Placed carefully, such devices provide little or no indication of an impending attack,” the report said.

Federal investigators believe one of the bombs that exploded at the Boston Marathon on April 15, 2013, was likely carried in this backpack. (Photo: FBI)

But since the other attacks, authorities noted, the design has been widely circulated and could have been picked up by an independent operator – a lone wolf.

The Pakistani Taliban, which claimed responsibility for the 2010 attempt in Times Square, has denied any role in the Boston Marathon attack.

Regardless, Suffolk County, Mass. District Attorney Daniel Conley said someone will pay for Monday’s attack.

“Make no mistake an act of cowardice and of this severity cannot be justified or explained. It can only be answered,” Conley said.

On Capitol Hill, Defense Secretary Chuck Hagel called the bombings “a cruel act of terror” and said “a thorough investigation will have to determine whether it was planned or carried out by a terror group, foreign or domestic.”

Boston Police Commissioner Edward Davis said investigators gathered a large number of surveillance video from businesses and intend to go through them frame by frame.

“It’s our intention to go through every frame of every video that we have to determine exactly who was in the area,” Davis said, calling it the most complex crime scene in history of the department. “Even as we were removing victims yesterday, officers were assigned to go into local establishments and secure those videos.”

Davis urged the public to try to get back to normal, but to keep eyes peeled for anything suspicious.

“We want you to live your life. We want you to be vigilant and there’s no reason to not come into the city, but we do have a threat and we’re working diligently to try and reduce that threat and we want you to go about your business. Give us a little room in Copley Square,” Davis said.

“There has to be hundreds, if not thousands, of photos and videos” that might help investigators, state police Col. Timothy Alben said.

Massachusetts Gov. Deval Patrick said contrary to earlier reports, no unexploded bombs were found. He said the only explosives were the ones that went off.

“Two and only two explosive devices were found yesterday,” Patrick said. “All other parcels in the area of the blasts have been examined but there are no unexploded bombs — there were no unexploded explosive devices found.”

“I think that happened as a result of some suspect packages that were disrupted. But we only have two devices that we’re aware of and both those devices were involved in the damage in the explosive incident,” ATF Special Agent In Charge Gene Marquez said.

Special Agent in Charge Richard DesLauriers said there are no known additional threats and agents are following a number of leads.

“We will go to the ends of the Earth to identify the subject or subjects who are responsible for this despicable crime, and we will do everything we can to bring them to justice,” said DesLauriers.

Overnight, authorities descended on an apartment complex in Revere, about a 20-minute drive from downtown Boston, where the FBI served a search warrant, WBZ-TV reported.

Massachusetts State Police confirmed that a search warrant related to the investigation into the explosions was served Monday night in Revere, but provided no further details.